Fluid pressure system and fluid flow control means therefor



May 23, 195o Filed Nov. 9, 1943 C. FLUID PRESSURE SYSTEM AND- FLUID FLOWCONTROL MEANS THEREFOR M. KENDRICK 4 Sheets-Sheet 1 INVENTQR CHA/nfs/I/. /ff/voe/c/f wf fw M* ff wf ATTORNEYS M'. KENDRICK May 23, 1950 FLOWCONTROL MEANS THEREF'OR Filed NOV. 9, 1945 BY Huma/Mv C. FLUID PRESSURESYSTEM AND FLUID 4 Sheets-Sheef 2 INVENTOR CHA @L 5 M /E ATTORNEYS` May23, 1950 c. M. KENDRICK l2,508,399

FLUID PRESSURE SYSTEM AND FLUID FLow coNTRoL MEANS THEREEUR Filed Nov.9, 1943 4 Sheets-Sheet 3 "n :15 ugr; iam

INVEN TOR A TTORNEYS May 23. 1950 c. M. KENDRICK 2,508,399

FLUID PRESSURE SYSTEM AND FLUID FLow CONTROL MEANS THEREFOR Filed Nov.9, 19215 4 sheets-skelet# A TTOHNEY5 Patentled 23, 1950 PRESSURE SYSTEMAND FLUID FLOW CONTROL MEANS THEREFOR Charles M. Kendrick, New York, N.Y., assignor to Manly Corporation, Washington, D. C., a

corporation of Delaware Application November 9, 1943, Serial No. 509,575

46 Claims.

This invention relates to iiuid pressure means and systems. It lsconcerned particularly with systems in which it is desirable to shut offthe flow of fluid through a line when the pressure in a portion of saidline is below a predetermined value, for example, in order to safeguardagainst material loss of the circulated fluid through escape thereoffrom the system in the event of rupture of a fluid conduit orother partofthe system and the invention relates stillmore particularly to themeans for safeguardingthe system against such loss of 'its circulatedfluid.

An important example of a fluid system of this character is an hydraulicsystem or circuit for aircraft use, and particularly for use in militaryaircraft. In such a system the rupture of a fluid conduit or other partof the system would, unless prevented, permit the escape of all thecirculated uid (except perhaps the small emervgency supply), and hencemight make it imposbe described in connection with such use but it Aimproved system of the character mentioned, to-` gether ywith simple andimproved means for limiting to a preferably relatively small andsubstantially predetermined amount, the volume of fluid* that may escapein the event of rupture of a part of the system.

Another `object is to provide an improved system of this charactertogether with improved means for limiting the loss of uid therefrominthe event of rupture of part of the system or circuit which is simpleand `reliable and which may be arranged to provide relatively little orno resistance to flow under normal operating conditions. A

Other objects will appear from the description and explanation whichfollow: v

The invention will be better understood from consideration of theaccompanying drawings which illustrate by wayof example severalembodiments of the present invention.

In the accompanying drawings:

Fig. 1 is a diagrammatic view, partly in section, of a fluid system orcircuit embodying the present invention;

Fig. 2 is an enlarged longitudinal sectional view of one of theelements, for convenience termed a circuit guard valve, of the systemshown in Fig. 1;

Figs. 3 and 4 are enlarged sectional views illustrating modied forms ofthe circuit guard valve means according to the present invention;

Fig. 5 is a fragmentary diagrammatic View, partly in section, showing amodified arrangement of a 'portion of the fluid circuit or system ofFig. l, but drawn to a scale different :from that of Fig. 1;

Fig. 6 illustrates, on an enlarged scale but dif yferent from that ofFigs. 2 and 3, partly in section, another modified form of the circuitguard valve means according to the present invention, which isparticularly suited for use in an inlet conduit leading to the selectoror reversing valve, but not limited to such use, together with theschematically illustrated modified form of the cooperating selectorvalve means andA certain portions of the fluid circuit;

Fig. 7 is an enlarged view drawn to substantially the same scale of Fig.2, partly in longitudinal section, illustrating a further modified formof the circuit guard valve means according to the present invention;

Fig. 8 is a diagrammatic view, partly in section, showing the fluidsystem or circuit of Fig. 1 as modified when the circuit guard valvemeans of Fig. 7 are employed therein;

Fig. 9 is an enlarged longitudinal sectional view drawn to a scalesubstantially the same as that of Fig. 7, illustrating a still furthermodified form of the circuit guard valve means according to the presentinvention;

Figs. 10 and l1 are fragmentary views, partly in section, drawn to thesame scale as that of Fig. 2 and illustrating modifications of thearrangement shown in Fig. 2;

Fig. 12 is an enlarged view, partly in section and partly diagrammatic,illustrating another modified form of the circuit guard valve meansaccording to the present invention; and

' Fig. 13 Yis a View, partly in section, diagram matically illustratinga modified arrangement for controlling a certain portion of the downwardmovement of the valve piston means of the modified circuit guard valvemeans of Fig. 12.

Referring now to these drawings, in Fig. 1, I have diagrammaticallyillustrated the present inexample as a rotary uid motor, but for con- Yvenience is here schematically illustrated as of the reciprocating typecomprising a piston Il) reciprocable in a cylinder I2 and having apiston rod II extending through the cover member I3 of said cylinder I2for connection to the device to be actuated thereby. Packing of anysuitable type. not shown, may be used to prevent the leakage of iiuidpast the piston I and around the piston rod II in conventional manner.

Pressure iluid for actuating the motor B is supplied from any suitablesource, not shown, through line or passage I5 which connects with theinlet port 25 of the selector valve A. The selector valve A is alsoprovided with a pair of cylin der ports 26 and 21 respectively, whichconnect with a pair of lines or conduits broadly designated by thenumerals I6 and I1 respectively, leading to the opposite ends of thecylinder I2. The selector valve A is further provided with an exhaust orreturn port 28 connecting with an exhaust line or passage I8 which maylead to a reservoir or the -flikenot shown. 'I'he selector' valve A alsoincludes a rotatable valve body 24 which, in the position in which it isshown in Fig. l, connects the inlet port 25 with the cylinder port 26and also connects the cylinder port 21 with the exhaust port 28, so thatthe flow of iiuid through the system is then as indicated by the arrowsin Fig. 1, the piston I0 of the motor B being moved toward the covermember I3. Rotation of the valve body 24 through 90 reverses theconnections above described and causes the iluid to flow through thesystem in a direction opposite to that of the arrows in Fig. 1;'thepiston I0 of the motor B is then moved toward the closed end of thecylinder I2. Rotation Aof the valve body 24 through approximately 45from the position in which it is shown in Fig. 1 cuts oil communicationbetween all of the ports of the selector valve A and hence stops andprevents movement of the piston I0 of the motor B.

The fluid system of Fig. 1 also includes two units of the improved meansaccording to the present invention for limiting to a preferablyrelatively small and substantially predetermined amount the volume offluid that may unintentionally escape in the event of rupture of certainparts of the system. These units, which for convenience aretermedcircuit guard valves, are

designated by the numerals 30 and 30 respectively and are here shown asdisposed in the conduits I6 and I1 respectively. These circuit guardvalve means or units, when employed as here shown, are preferablydisposed as close as possible to the selector valve A in order toprovide protection against loss of iiuid because of rupture of as muchof the system as possible, as will be more fully understood from thefurther explanation which follows. The portions of the conduits I6 andI1 respectively intermediate the selector valve A and the units 30 and30' respectively, for convenience are designated lby the referencenumerals I6A and I1A respectively, and similarly the portions of theseconduits intermediate the circuit guard units 30 and 30 respectively,and the motor B are designated by the numerals I6B and I1B respectively.

The circuit guard valve units 30 and 38' are schematically shown in Fig.las identical, al-

though not necessarily so, and their construc-l tion and arrangementwill be understood from/f*l consideration of the sectional view of thecircuit valve unit 3|! as shown in Fig. 2. Referring now to Fig. 2,circuit guard valve unit 30 includes a housing broadly designated by thenumeral 3l having a longitudinal bore 32 which terminates at its innerAend ina valve seat 33 of any suitable type or contour. The outer end ofthe bore 32 is provided with a gland 34 which is held against inwarddisplacement by a shoulder 35 and is also held against outwarddisplacement 'by a cap member 10 in threaded engagement with theenlarged outer end of the bore 32, suitable packing 36 being used toprevent the escape of fluid. 'Ihe portion of the bore 32 intermediatethe valve seat 33 and the inner end of the gland 34 is for conveniencetermed the chamber 38 and is suitably connected with the portion I6-A ofthe conduit I6 as by a transverse passage 39 in the -boss 48. Thehousing 3| also includes a throat 42 for the valve unit which isdisposed closely adjacent the valve seat 33 and connects with the bore32. In the embodiment of Fig. 2, the throat 42 is of the same diameteras that of an intermediate chamber or bore 4I, the upper end .of whichconnects with the valve throat 42 and the lower end of which connectswith a bore 44 of larger diameter which serves as the cylinder for thedash-pot piston 60 to be presently described. The bore 4I is suitablyconnected with the portion I6-B of the conduit I6, as by'a transversepassage 45 in the boss 46. The lower end of the bore 44 is suitablyclosedas by a cap 41 here shown as in threaded engagement with thehousing 3|, suitable vpacking 48 being used to prevent the escape offluid.

The circuit guard valve 30 of Fig. 2 also includes a valve pistonbroadly designated by the reference numeral 5Il having a hollow stemportion 5I by which said valve piston 50 is slidably supported in the-central opening of the gland 34, suitably packing 52 being used toprevent the leakage of fluid. The stem 5I terminates at its lower end ina head 53 which is disposed in the chamber 38 and which is adapted toengage the valve seat 33 in fluid tight engagement therewith when thevalve piston 58 occupies its extreme inward or fully closed position. Acylindrical shoulder 54 extends downwardly from the head 53 andterminates in a reduced end portion 55 of the valve piston 58, thearrangement being such that said end portion 55 is in contact with theupper end of the dash-pot piston 6U when the parts are in the positionillustrated in Fig. 2, as clearly shown by this drawing. The shoulder 54is made of a diameter greater than the diameter of the stem 5I butsomewhat less than the diameter of the throat 42 of the valve unit, fora purpose to be later explained. y

The circuit guard valve unit 30 also includes a dash-pot piston 60 whichis slidably disposed `in the bore 44 and is here shown (Fig. 2) asprovided with suitable packing 6I to prevent the escape of fluid pastthe dash-pot piston 6U from 'the outer end of the bore 44, that is tosay, from the end of said bore 44 intermediate said dash- .pot piston 60and the cap 41. A spring 63 urges said dash-pot piston 60.

A uid connection under control of a vone-way instance, the latterarrangement frequently having the advantages of compactness and lowweight which are of importance particularly for aircraft use. Thedash-pot piston 60 is accordingly shown in Fig. 2 as provided with acentral longitudinal passage broadly designated by the numeral 64, whichpassage contains a check valve broadly designated by the numeral 65, theupper end of the passage 64 being of reduced diameter and connectingwith a transverse passage 66 in the reduced end portion 61 of the valvepiston 60. With this arrangement fluid may pass through the passages 66and 64 into the outer end of the bore 44 but the check valve 65 preventsthe passage of uid in the opposite direction; the check valve 65 ispreferably made such as to present very little resistance to the passageof fluid into the outer end of the bore 44 in order that fluid mayfreely pass into said outer end of said bore 44 whenever the pressuretherein is less than the pressure in the bore 4I.

A restricted and always open iluid connection is also provided betweenthe outer end of the bore 44 and the bore 4I and this likewise may be ofany preferred suitable arrangement; for example, this restricted passagemight be provided by limited clearance between the bore 44 'and thedash-pot piston 6|) with the packing 6I omitted. As shown in Fig. 2,however, this restricted connection takes the form of a small passage 68formed in the dash-pot piston 60 and connecting with the passage 64 at apoint lower than the position of the check valve 65, it being understoodthat this passage 68 is here intended to represent all restrictedconnections suitable for the purpose to be later explained.

The valve piston 50 of the circuit guard valve unit 30 is arranged to bebiased toward the position in which it lis shown in Fig. 2 and to bemoved into this position whenever the pressure in both the chamber 39and the bore 4i are at or below predetermined values. As shown in Fig.2, two springs are employed for this purpose in the circuit guard valveunit 30, one of these springs being the spring 63 which, as alreadyexplained, urges the dash-pot piston 60 toward its extreme inwardposition of Fig. 2, said spring 63 also acting through said dash-potpiston 60 to urge the valve piston 50 toward its position of Fig. 2whenever said valve piston 50 occupies a lower position. A second spring13, disposed in the interior of the cap member 1li, acts to urge thevalve piston inward to the position of Fig. 2 whenever said valve piston50 occupies a higher position, but said spring 13 does not urge saidvalve piston 50 to a position lower than that of Fig. 2. For thispurpose the outer end of the spring 13 acts against the end 1I of thecapmember and the inner or lower end of said spring 13 acts against anabutment piece or spring retions 'in Fig. 2 but the lower end of the cup16 comes into contact with the upper. end of the gland 34 when thisposition of the cup and plston is reached, thus limiting the extent towhich said cup and piston may be urged or moved inward by said spring13. n With the arrangement of Fig. 2 as above described, the valvepiston will be moved into the position in which it is shown in Fig. 2whenever the conduit I6 is connected with the return conduit I8 (andafter exhaust of uid i through the conduit I6 has ceased), hence saidvalve piston 50 will always occupy this position when the valve body 24of the selector valve A is turned to establish fluid connection betweenthe inlet conduit l5 and said conduit I6. Pressure fluid entering theconduit i6 first passes into the chamber`38 of the circuit guard valveunit 30, the passage of this fluid, which is frequently a liquid, such,for example, as oil, encountering substantially little or no resistanceto flow up to this point. With the valve piston 50 in its position/ofFig. 2, however, the shoulder 54 thereof extends into the throat 42 ofthe valve unit and hence provides a restricted connection between thechamber 38 and the bore 4i, this restricted connection presentingresistance to flow therethrough with respect to the full volume of fluidadmitted to the conduit I6 but said restricted connection permittingsome iluid to pass into the bore 4|. This restricted connection :in thepresent instance thus comprises the space between the shoulder 54 andthe throat 42 of the valve unit and it will be understood that anysuitable form of restricted connection may be employed between thechamber 3B and the bore 4| during the interval of the retarded downwardmovement of the valve piston 50 from its position of Fig. 2, to bepresently described, or during a corresponding interval.

If the portions of the circuit or system intermediate the throat 42 andthe piston I0 of the motor B are filled with fluid, as will normally bethe case, and if these portions of the circuit are intact (i. e. freefrom rupture), the pressure fluid passing into the bore 4I through thisrestricted connection will almost immediately build up pressure thereinwhich will act upon the lower end of the valve piston 50 and move thelatter against the resistance of the spring 13 into said valve pistonsextreme upper or fully open position, where it will present little or noresistance to the ow of fluid through the valve unit 30. AS clearlyshown in Fig. 2, the upper end of the stern 5I of the valve piston 50 isexposed to atmospheric pressure, this being assured in the presentinstance by the hole 18 in the disk member 18 which will be laterdescribed. The valve piston 50 will remain in its uppermost position aslong as the pressure in the chamber 38 and in the bore 4I exceed thevalue determined by the spring 13, irrespective of the volume of fluidpassing through the valve unit 3B and irrespective of the time that suchpressure exists.

If the portion of the system intermediate the throat 42 of the valveunit and the piston I0 of the motor B is not filled with fluid (asbecause of leakage from this portion of the circuit due to rupturethereof or otherwise) at the time that pressure fluid is first admittedto the chamber 38, the fluid that immediately passes through therestricted connection between the chamber 38 and bore 4i will be unableto immediately build up pressure in said bore 4I. Under this conditionthe valve piston 50 will be urged downkward toward the seat 33 by actionlof the presby the restricted connection between said chamber 38 and thebore 4 I. The downward force thus exerted on the valve piston 50 isequal to the force exerted by the pressure fluid in the chamber 38 uponan area equal to the difference between the cross-sectional area of theshoulder 54 and the cross-sectional area of the stem 5|. In thisconnection it will be recalled that the diameter of the shoulder 54 isgreater than that of the stem but less than that of the throat 42 of thevalve unit, and the reason for these relative proportions will now beunderstood. The hydraulically-imposed downward force just described thusacts to move the valve piston 50 downward but such movement is resistedby dash-pot action of the dash-pot piston $8 which can be moved downwardby said valve piston 50 only as rapidly as permitted by the escape ofiiuid through the restricted passage 68 in said dash-pot piston 60. Acontrolled interval is thus provided between the time that the valvepiston 50 commences its downward movement from its position of Fig.'2and the time that said valve piston 50 reaches its extreme downwardposition in which the head 53 engages the seat 33 to out off all fluidconnection between the chamber 38 and the bore 4|, and during thisinterval fluid continues to pass into the bore 4| through the restrictedconnection between the throat 42 and shoulder 54. The volume of fluidthus permitted to pass into the bore 4| after the valve piston 50 startsthe above mentioned downward movement is determined by the size of therestricted connection between the chamber 38 and bore 4| and also by thesize of the restricted passage 68 in the dash-pot piston 6D, and hencemay be made substantially any desired amount.

The maximum volume of fluid which is permitted to pass into the bore 4|during the interval of the retarded downward movement of the valvepiston 50 will thus be a substantially predetermined amount and thiswill be the case, closely approximately if, indeed, not exactly, underall operating conditions. In this connection it may be pointed out thatthe pressure in the lower end of the bore 44 intermediate the dash-potpiston 60 and the cap 41 is determined by the force exerted upon saiddash-pot piston 68 by the valve piston 50, and the pressure existing insaid outer end of said bore 44 determines in part the rapidity withwhich fluid will pass outward therefrom through the restricted passage68; the spring 63 presents, of course, some resistance to downwardmovement of the dash-pot piston 60 but considerably less than is imposedby the fluid in the louter end of said bore 44 in the preferredarrangement. The downward force exerted on the dash-pot piston 60 by thevalve piston 50 is in turn determined, however, by the pressure existingin the chamber 38 which pressure also determines the rapidity with whichfluid will pass through the restricted connection between said chamber38 and said bore 4|. A relation thus exists between pressures in thechamber 38 and in the outer end of the bore 44, although the pressure inthe latter will be considerably lower than the pressure in the former inthe arrangement of Fig. 2. Change in fluid pressure in the chamber 38will thus result in corresponding change in the pressure of the iiuid inthe outer end of the bore 44, so that the rapidity with which iiuid o!any given viscosity can be exhausted from the outer end of said bore 44through the restricted passage 68 will change correspondingly with therapidity with which fluid is passing from the chamber 38 into the bore38 through the restricted connection therebetween. Similarly. change inviscosity of the uid will simultaneously and correspondingly (althoughnot necessarily exactly) change the resistance to passage thereofthrough the restricted passage 88 and the restricted connection betweenthe chamber 38 and bore 4| respectively. The maximum volume of fluidpermitted to pass into the bore 4| during the interval of retardeddownward movement of the valve piston 50 from its position oi Fig. 2until said valve piston 50 reaches its extreme downward position maythus be limited to practically any substantially predetermined amount byproper proportioning of the several cooperating parts and passages, butsuch maximum volume is preferably kept as small as practical in theindividual case, and frequently this will be very small, but saidmaximum volume is always preferably relatively small in relation to thetotal available supply of fluid.

If the portion of the system intermediate the throat 42 of the valveunit 30 and the piston I0 of the motor B has been ruptured at any pointtherein, as by a bullet or otherwise, the fluid passing into the bore 4|during the above described interval of retarded downward movement of thevalve piston 5|)v will be unable to build up pressure in this portion ofthe system and hence the valve piston 50 will move to its extremedownward position so that the head 53 comes into engagement with theseat 33 and prevents the furthe;` passage of fluid through the valveunit 30. The volume of fiuid that may be unintentionally lost underthese conditions is thus limited to the amount passing from the chamber38 into the bore 4| through the restricted connection therebetweenduring the above mentioned interval and the system is safe-guardedagainst further unintentional uid loss. But if there has merely beenleakage out of the portion of the system above mentioned, the fluidpassing into the bore 4| will replenish the supply of iiuid therein andwill then almost instantly build up pressure in the bore 4| which willact on the lower or inner end of the valve piston 50 and move said valvepiston into its extreme upper position, in the same manner as if thispart of the system had been completely lled with fluid at the time ofadmission of pressure iiuid to the chamber 38. It may also be pointedout here that the valve piston 50 will be reset Ato its position of Fig.2 upon connection of the conduit I6 with the return conduit I8, and suchresetting will recur each time that this connection is reestablished.For example, if the valve piston 50 is in its extreme upper or fullyopen position at the time the connection is established between theconduits I6 and I8, the spring 13 will act to instantly move said valvepiston 50 downward into its position of Fig. 2. If, however, the valvepiston 58 then occupies its extreme downward position or any positionbelow that of Fig. 2, said valve piston 58 will be instantly movedupward to its position of Fig. 2 by the spring 83 acting through thedash-pot piston 60, so that both pistons will be restored to theirpositions of Fig. 2. Upon such upward movement of the dashdot piston 60the check valve 65 opens to permit uid to quickly enter the outer end ofthe bore 44 so that upward movement of the dash-pot piston 60 may bevery rapid, and it is for this reason that the check valve II isprovided. The pilot or operator may thus reset the valve piston 50 toits position of Fig. 2 as many times as desired by vmerely turning thevalve body 24 of the selector valve A to establish connection betweenthe conduits I6 and I8. and for each such setting or resetting the guardvalve unit 30 will 'permit the substantially predetermined volume offluid to pass into the bore 4I unless pressure is built up therein toopen the valve by moving the valve piston into its extreme upperposition, and the pilot may thus cause the admission of as much fluid asdesired into the portion of the system intermediate the throat 42 andpiston II) of the motor B, with the result that movement of said pistonI may be provided under almost all conditions in which the system isintact or the pilot may assure himself that failure of the motor B torespond is due to rupture of the system or the like and not merely toexcessive leakage of iiuid therefrom. In many instances, therefore, thearrangement may be made such that the maxifmum volume of fluid passinginto the bore 4I during the above described retarded downward movementof the valve piston 50 is merely enough to replenish normal leakage fromthe system due to defective packings or the like, and this amount can bemade very small in many instances. This is the preferred arrangement butit will be understood that thismaximum volume may be made of any desiredamount as preferred or as occasion may indicate to be advisable.

If rupture occurs in the portion of the circuit .intermediate the valveseat 33 and the piston III of the motor B during the time that the inletconduit I is connected with the conduit I6, the pressure in said conduitI6 will drop and the valve piston 50 will first be moved to its positionof Fig. 2 by the spring 13, after which it will move downward, at therelatively retarded rate of movement determined by the dash-pot piston60, until the head 53 comes into engagement with the valve seat 33 andcuts oif all fluid communi-v ythe motor B if the system is 'in goodorder.

In some instances there may be a tendency for the actuated memberattached to the piston rod I I of the motor B to move the piston IIlthereof more rapidly than said piston can be moved by the pressure fluidadmitted to the cylinder I 2- from the source of such pressure fluid,with the result that such movement or overrun of the piston I0 wouldtend to create a vacuum in the part of the circuit connected with theintaking side of 4the motor B and the latter condition might also tendto retard such overrunning movement of the piston I0 which might not bedesirable. An instance of this kind is found in connection with thehydraulic motors employed to retract and extend the landing gear of someaircraft, in which gravity action tends to extend the landing gear intoproper position for landing and in which it is frequently desirable thatsaid landing gear be permitted to move toward or into its fully extendedposition as freely and as rapidly as possible under such gravity action.For purposes of illustration, let it b e assumed that the motor B ofFig. I is employed to actuate such aircraft landing gear and that thearrangement is such that movement of the piston I0 thereof toward thecover member I3 is the direction of its movement to extend the landinggear into position for landing, and also that said landing gear undergravity action tends to move into this position more rapidly than suchmovement can be eifected by action upon the piston I0 of the pressurefluid admitted through the conduit I6 to the cylinder I2 so that saidpiston I0 tends to overrun. In such instances and as illustrated in Fig.1, I preferably provide a connection, such as the passage I9, betweenthe return conduit I8 and the portion IB-B of the conduit I6, with acheck valve 2li therein arranged to permit uid to pass freely throughsaid passage I9 into said portion I B-B but preventing the passing offluid in the opposite direction. With this arrangement when overrun ofthe piston Ill tends to create a, vacuum in the conduit I6, fluid willpass into the portion IB-B thereof as rapidly as required to keep saidconduit completely filled so that there will be no cavitation in thispart of the system. The circuit guard valve unit 30 is then preferablymade such that the interval of retarded downward movement of the valvepiston 50 from its position of Fig. 2 is somewhat longer than themaximum time in which overrun of the piston I0 of the motor B can takeplace. The fluid passing into the bore 4I during this interval willalmost instantly build up the pressure required to move the valvepiston. 50 upward, to thereby fully open the circuit guard valve 30, assoon as overrun of the piston I0 ceases yand said piston I Il will thencontinue its movement substantially without interruption under action ofthe pressure fluid admitted to the cylinder I2 through the conduit I6.This arrangement also provides added safety in the event of failure ofthe entire hydraulic system as it permits the piston I0 to move freelyunder gravity action of the landing gear due to the ready admission offluid to the intaking side of the cylinder I2, thus permittingsubstantially free extension movement of the landing gear under gravityaction.

Up to this point the action of the circuit guard valve 30 has beenconsidered only from the standpoint of ilow of the fllulii/ from theselector valve A to the motor B. the reverse direction of flow, thevalve piston 50 of the valve unit 30 will be moved upward from itsposition of Fig. 2 by action of the fluid exhausted by the motor B uponthe lower or inner end of said valve piston 50. In order to keep theback pressure as low as possible, the arrangement is preferablymade suchthat the valve piston 50 will be moved toward or into-its extreme upperposition by action on the inner end thereof of fluid having a pressureequal to or less than the back pressure caused by flow of the exhaustedfluid through the selector valve A, this being accomplished by properproportioning of the parts, including the spring 13. In some instances.however, it may be desired to make the arrangement such that arelatively high pressure, in excess of the normal back pressure causedby flow of the exhausted fluid through the selector valve A, is requiredto move the valve piston 50 upward from its position of Fig. 2 into itsuppermost position. yet it may also be desired to avoid the consequentlyhigh back pressure that would result when uid is exhausted through thecircuit guard valve under this condition. In such instances a by-passline, including a check valve,

may be provided around the circuit guard valve. An arrangement ofthischaracter is illustrated in connection with the circuit guard valve30' of Fig. 1, in which the by-pass line 2| is provided around saidvalve unit 30', said by-pass line 2| being provided withl a check valve22 which permits uid to pass therethrough toward the selector valve Abut prevents iluid ow therethrough in the opposite direction.

The valve piston 50 of the circuit guard valve unit might tend tointerfere with illling or bleeding of the circuit or system and meansare accordingly provided by which said valve piston 50 may be held inits extreme upper position during these operations or whenever sodesired. As shown in Fig. 2, the hollow stem 5| of the valve piston 50is provided with one or more radial holes 56 into which a suitablyformed hook may be inserted, and for this purpose the end 1| of the cap10 is provided with a hole 12 through which said hook may be passed. Asalso shown in Fig. 2, the shoulder or flange 15 of the cup 14 terminatesadjacent the inner circumference of the hollow stem 5| and hence doesnot interfere with the insertion of the hook. A disk 16 covers the hole12 in the ,cap and is suitably attached to said cap 10 as by means of apost 11 upon which said disk may be pivotally mounted.

The circuit guard valve 30 according to the present invention has manyadvantages, some of which have already been pointed out. Among these areits simplicity, compactness and dependability. Another is its lightweight which is particularly important for aircraft use, and circuitguard valve units for this purpose may be constructed so that the weightof each is only a few ounces.

Fig. 3 illustrates a modiiled form of the circuit guard valve accordingto the present invention which will answer requirements in manyinstances and may be preferred because of its somewhat smaller size andcorrespondingly lighter weight. As illustrated in Fig. 3 the modifiedvalve unit |30 is shown as connected with the portions |6A and |6-B oithe conduit I6 of Fig. 1, although it can also be used in place of thevalve unit 30' of Fig. 1 or elsewhere in the circuit as will be laterexplained. In this instance the spring 13 is alone employed to urge themodified valve piston |50 `toward its position of Fig. 3 and to resetsaid valve piston to this position whenever the conduit I6 is connectedwith the return conduit I8. For this purpose the modied cap member |10is provided at its outer end with an annular flange |13 which acts as astop for an abutment piece |12 at the outer end of the spring 13, thearrangement being such that said abutment piece |12 may move inward withrespect to said flange. The inner end of the spring 13 bears against acup member |14 generally similar to the spring retaining cup 14 oi Fig.2, though of different proportions.

A rod |80 extends through the central opening in the abutment piece |12and projects into the hollow stem |5| of the valve piston |50. The innerend of the rod |80 is threaded to receive a nut |8| and a `1am or locknut |82 and the nut |8| is arranged to bear against a washer |83 whichin turn bears against a retaining ring |84 which is snapped into asuitable groove in the stem |5|.

The outer end of the rod |80, here shown as of larger diameter than theinner end thereof, is likewise threaded to receive a preferably knurlednut |85 and a jam or locking nut |86 and these nuts are so adjusted thatthe nut |85 is in contact with the abutment piece |12 when the parts arein the position shown in Fig. 3. A rubber ring |81 or other suitablefriction or locking device is provided to hold the rod againstunintentional movement with respect to the abutment piece |12; as thering |81 might tend to form a seal around the rod |80 and thus preventthe entry of air, the abutment piece |12 is also provided with a hole|18 to assure that the outer end of the valve stem |5| is exposed toatmospheric pressure. With this arrangement upward movement oi' thevalve piston |50 from its position of Fig. 3 merely raises the cup |14and compresses the spring 18 toward the abutment piece |12, saidabutment piece |12 and the rod |80 remaining stationary. Upon downwardmovement of the valve piston |50 from its position of Fig.

3, the washer |68 engages the nut |8| so that the rod |80 is. moveddownward, causing similar downward movement of the abutment piece |12and compressing the spring 18 toward the cup member |14.

The rod |80 and its associated parts may also be employed to move andhold the valve piston |50 above its position of Fig. 3 during filling orbleeding of the circuit, etc. To move the valve piston upward from itsposition of Fig. 3, the mechanic merely grasps the nut and pulls the rod|80 outward. the valve piston |50 being moved outward correspondingly bynuts, etc., at the inner end of said rod |80. After the filling,

-bleeding or other operation is completed, the

nut |65 or rod |80 is pushed inward so that the parts resume theirposition oi Fig. 3.

The modified valve piston |50 is also provided with a head |60 whichserves as the dash-pot piston in this embodiment and is arranged toenter the bore |44 which is closed on its outer end and which serves asthe dash-pot cylinder. As shown in Fig. 3, the arrangement is such thatthe head |60 just begins to enter the bore |44 when the parts are in theposition of Fig. 3 in order to permit the valve piston |50 to be moveddownward to this position quickly and also to assure that the dash-potaction will produce the desired interval of retarded downward movementof the valve piston |50 as said valve piston is moved downward from itsposition of Fig. 3. For the same reason the modified chamber or bore |4|of the modified housing i3| is here shown as oi larger diameter thanthat of the bore |44 and the two bores are preferably joined by atapered portion |43. For purposes of assembly the diameter of the head|60 is made just slightly smaller than the diameter of the throat 42 ofthe valve unit and the arrangement is also preferably such that the headI 60 does not project above the lower side of the passage 45 when thevalve piston |50 is in its uppermost position in order not to interferewith the flow of fluid into said passage 45.

Any suitable form of restricted passage ybetween the bores |4| and |44may be employed in order to provide a restricted path of escape for thefluid in the outer end of the bore |44 in order to provide dash-potaction as the head |60 moves downward therein to the desired interval ofretarded downward movement of the valve piston |50 from its position ofFig. 3 to its fully closed position. For example, this restrictedpassage might take the form of a hole through the head |60 or otherparts oi' the structure. As here shown, however, a small clearance isprovided between the circumference of the head |60 and the bore |44 andthis clearance is utilized as the restricted passage, so that the amountof this 13 clearance determines the relative rapidity with which fluidcan be exhausted from the lower end of bore |44 as the head |60 movesdownward therein. This arrangement has the advantage of simplicity andalso reduces the frictional resistance to movement of the valve piston|50 as no packing is used for the head |60. It will also be observedthat the restricted passage between the bores |44 and |4| provided bythis clearance space is generally similar in form and arrange ment tothe restricted passage or connection between the chamber 33 and the bore|4| provided by the clearance space between the shoulder 54 and throat42 of the valve unit, so that both of these restricted connections willhave generally similar if not identical characteristics.

The modified valve piston |50 is also provided with a longitudinalpassage |64 which extends from the lower end of the head |60 into thereduced portion |65 of said valve piston intermediate the shoulder 54and head |60. The passage |64 connects with a transverse passage |66 inthe reduced portion |55 of the valve piston and the passage |64 is alsoprovided with a check valve indicated broadly by the numeral |65 whichis arranged to permit fluid to pass therethrough toward the outer end ofthe bore |44 but prevents the passing of fluid in the oppositedirection. This arrangement is providedto permit fluid to freely enterthe outer end of the bore |44 when the head |60 is therein whenever thepressure in the bore |4| exceeds the pressure in the bore |44, tothereby permit quick upward movement of the valve piston |60 so thatsaid valve piston |60 may be quickly reset to its position of Fig. 3from any lower position which it might occupy at the time the conduit I6is connected with the return conduit I8 and also to permit said valvepiston |60 to be moved quickly upward whenever the pressure in thechamber 38 and bore |4| exceeds the value required to efl'ect suchmovement. l

The functioning of. .this modified circuit guard valve unit |30 of Fig.3 is generally similar to that of the unit 30 of Fig. 2 and will beunderstood from the explanation previously given.

The circuit guard valve units may be modified in other ways, such forexample as shown in Fig. 4 in which the modified valve unit 230 is shownas connected with the portions |6-A and IE-B of the conduit |6 and theparts are shown in the positions which they occupy when said conduit I6has been connected with the return conduit I and no fluid is flowingtherethrough.

In this modied form the modified valve piston 250 is slidably supportedby its stem 25| in the central. opening of the modified gland 234,suitable packing being employed to prevent the outward leakage of nuidas indicated at 236 and 252 respectively. The modified gland 234 is heldagainst inward displacement by a shoulder 235 and is also held againstoutward displacement by a plug or cap member 210, here shown as hollowto accommodate part of the spring 213 which urges the valve piston 250the full distance toward its seat 233 in the modied housing 23|. 'I'hecap or plug 210 is also shown as provided with a hole 212 in the topthereof through which a suitable hook or the like may be inserted into ahole 256 in the upper end of the preferably hollow stem 25| so that thevalve piston 250 may be held o its seat 233 during filling or bleedingoperations, etc.; the hole 212 also assures that the outer end of thevalve stem 25| is at all times exposed to atmospheric pressure. In orderto assure that the valve piston 250 is not raised of! itc seat 233 byhydraulic action when pressure exists in'the chamber 238 andsubstantially no pressure exists in the bore 24| below the valve seat233, the stem 25| is made of a diameter equal to or less than thediameter of the sealing contact between the head 253 of the valve piston250 and the seat 233, and as here shown these relative proportions areassured by making the diameter of the stem 25| equal to the diameter ofthe throat 242 of the modified valve unit 230. With this arrangement,the valve piston 250 will be moved substantially instantly to bring thehead 253 into sealing engagement with the seat 233 whenever, for anycause, the pressures in the chamber 236 and bore 24| drop below thevalue determined by the spring 213.

As in embodiments previously described, means are provided formaintaining during a substantially predetermined interval a restrictedfluid connection between the chamber situated above the valve seat andthe bore situated below said valve seat in order that a substantiallypredetermined maximum volume of fluid may pass into said bore before allfluid connection between said chamber and said bore is cut ofi, theinterval above mentioned immediately following the increase of pressurein said chamber above the pressure existing in said bore after thepressure in both said chambers and said bore have dropped to a valuebelow the value determined by the spring that urges the valve pistoninward and while the pressure in said bore remains below the valuerequired to move the valve piston upward. In the embodiment of Fig. 4the means just mentioned are separate from the valve piston means andwill now vbe described.

As shown in Fig. 4 the modified housing 23| is provided with a bore 244closed on its lower end and having an enlarged upper end portion 245which is suitably closed as by a plug 241. The chamber 230 is suitablyconnected with the enlarged upper end 245 of the bore 244 as by atransverse passage 239, here shown as an extension of the passage 39 inthe boss 40. The bore 244 is also provided with a counterbore 246 whichis suitably connected with the bore 24| as by a transverse passage 243,here shown as drilled from the side of the housing 23| adjacent the bore244 and closed by a plug 246. Disposed within the bore 244 and extendinginto the enlarged upper end 245 thereof is a cylinder member 260 closedon its upper end except for passages to be presently described and heldin position against a disk 249 at the lower end of the bore 244 as by asuitable spring 259 which acts against the upper end of said cylindermember 260 and the plug 241. As illustrated thecylinder member 260 hasan outer diameter substantially the same as that of the bore 244 andsuitable packing 26| is provided to form with the outer circumference ofsaid cylinder member 260 a fluid tight seal between the enlarged upperend 245 of the bore 244 and the counterbore 246 therein.

Slidably fitted within the bore of the cylinder member 260 is a piston280, here shown as hollow to receive a spring 289 which urges saidpiston 280 toward its extreme upper position in which it is shown inFig. 4 and substantially instantly moves said piston 280 into thisposition whenever fluid pressures acting on the opposite ends thereofare substantially equal. The lower end of the spring 289 acts against asuitable abutment piece 201 in the bore of the cylinder member 260 andwhich is here shown as held in position by aaoasec a retaining ring 286;the abutment piece and retaining ring also act as a stop which limitsthe downward movement of th piston 280. Fluid may be quickly and readilyexhausted from the upper end of the bore of the cylinder member 260 uponupward movement of the piston 280 therein through the longitudinalpassage 264 which is provided with a check valve 265 arranged to permitiiuid to pass in this direction but preventing the passing of fluid inthe opposite direction.

Other features of construction and arrangement of the cylinder member260 and piston 280 will be understood from anexplanation of the mannerin which they function. For: purposes of explanation, it will be assumedthat the pressure in the bore 24| is less than the pressure required tomove the valve piston 250 ofi its seat and also that the pressure in thechamber 238 has just increased above that in said bore 24|. Theconditions just mentioned would come about, for example, almostimmediately following the establishment of iiuid connection between theconduit I6 and the inlet conduit i5 or following a rupture in the systemintermediate the valve seat 233 and the piston i of the-motor B duringthe time that the conduit I6 is connected with the inlet conduit I andafter the pressure in said chamber and in said bore had first dropped toa value such that the spring 213 had moved the valve piston 256 into theposition in'which it is shown in Fig. 4.

Referring to Fig. 4, under the conditions just mentioned pressure fluidfrom the chamber 238 would pass through the passage 239 into theenlarged upper end 245 of the bore 244 and thence through passages 262formed in the cylinder member 260 into an annular port or counterbore266 in the bore of said cylinder member 266.

With the parts in the positions of Fig. 4, a restricted fluid connectionis provided between the port 266 and an annular port region or port 261l of the bore of the cylinder member 260 which is connected with thecounterbore 246 of the bore 244 as by means oi radial passages 269 alsoformed ln the cylinder member 260. The restricted fluid connection justmentioned is here provided by the space between the bore of the cylindermember 266 and the reduced portion or neck 282 of the piston 280intermediate the head 28| at the upper end thereof and the head 283 atthe lower end thereof, and this restricted passage is such that theresistance to flow therethrough builds up a pressure in the enlargedupper end 245 of the bore 244 exceeding the pressure in the countcrbore243. Fluid may thus pass from the chamber 238 to the bore 24| as long asthis restricted connection remains open.

A counterbore 263 at the upper end of the bore of the cylinder member2661s connected with the enlarged upper end 245 of the bore 244 by arestricted passage 268.- Pressure iluid from the -chamber 238 may thusenter the counterbore 263 where it acts upon the upper end of the piston280 and moves said piston downward against the preferably relativelylight resistance of the spring 239. Fluid exhausted from the bore of thecylinder member 266 in advance of the piston 280 as said piston movesdownward may pass out through holes 284 formed in said piston 280substantially as shown. The piston 28|! will thus be moved downward butonly at a rate determined by the rapidity with which pressure uid entersthe counterbore 263 through the restricted passage 268. The piston 286will thus move downward relatively slowly until the longitudinal slots286 formed in the upper end of its head 26|. come into connection -withthe -port 266, when pressure fluid will be admitted rapidly to the upperendl of the piston 280 and rapidly moves said piston downward for theremainder of the distance to its extreme downward position in which thehead 28| enters the portion of the bore of the cylinder member 260intermediate the ports 266 and 261 therein, said head thus cutting oilfluid connection between said ports. The purpose of the longitudinalslots 286 is to provide relatively quick movement of the piston 260 asit comes into its extreme downward position to thereby assure that thefluid connection between the ports 266 and 261 is completely cut oi, andthat a small uid connection does not remain therebetween, but said slots28B may be omitted in instances where such rapid nal movement of thepiston is found to be not required to assure complete cut oil of thefluid connection between these ports.

A controlled interval is thus provided between the time that the piston288 starts and completes its downward movement, the greater portion ofwhich Yis :retarded movement. During this interval the restrictedconnection above described is maintained between the ports 266 and 2 61of the cylinder member 266 so that uid may continue to pass from thechamber 238 into the bore 24| during this interval. As explained, thisinterval, which will vary with pressure and viscosity of the fluid, iscontrolled by means of the restricted passage 268 and similarly thevolume of fluid passing from the chamber 236 to the bore 24| iscontrolled by the restricted passage between the ports 266 and'261 ofthe cylinder member 26|),V hence the maximum volume of uid permitted topass from said chamber to said bore is held to a substantiallypredetermined amount for each downward stroke of the piston 280. Themodified circuit guard valve 230 of Fig. 4 thus limits to asubstantially predetermined amount, which is preferably relatively smallin comparison with the total fluid supply available, the maximum volumeof fluid that may be unintentionally lost in the event of rupture of thecircuit intermediate the valve seat 233 in the housing 23| and thepiston I6 of the motor B, regardless of whether suchrupture occurs priorto connection of the conduit I6 with the inlet conduit i5 or at any timewhile such connection exists.

The valve piston 256 will be almost immediately moved upward from itsposition of Fig. 4, to thereby establish direct and substantiallyunrestricted iluid connection between the chamber 238 andthe bore 24|,whenever the pressure of the uid `in the bore 24| reaches a value suchthat the action thereof on the lower end of the valve piston 250 issufficient to overcome the forces acting to hold said valve pistons head253 in engagement with the valve seat 233. This will occur almostinstantly after the establishment of fluid connection between theconduit I6 and the inlet conduit i5 if the system has not been rupturedand is filled with fluid. It will also occur substantially immediatelyafter the passing (through the restricted connection between the ports266 and 261 of the cylinder member 266) of suflicient fluid to replenishany normal amount of leakage that may have taken place in the circuitintermediate the valve seat 233 and'the piston I6 of the motor B, aswill be understood from the explanation given in connection with theembodiment of Fig. 2. When( Sitloln' of Eie- 4 lishment off connection`between -theinIetcOnmarfoansolthe piston# 8Mo repeat its `downwardl,for each;y vsuch ,downward stroke of said-.- .piston to its :positionoIfFig. 4-,andsubsequentlynre-establishing connection between saidconduits Up -to thispoint the circuit: guardA valve units E?.,havebeenconsidered as disposedin the ycircuit ,f intermediate/theselectorfvalve Amand .themotor 1' asillustrated inFig.,il. Thiswillfrequently be i the most convenient locationl inthecircuit forvpositionsin the circuit or systemwA For example, g5 lthe circuitguardvalve units: may bedisposed in the inlet `conduit in advance Lofthe selector -valve as illustrated inl Fig. ingwhichfthe circuit i theseunits but theymayalsobelocated at other i guard `valve unit"30,identicalwith the unit `3|'I of j :Figs1. and 2,-is shown as. connected with apori .tion IS-Aof the inlet 'conduit |5,i the other u VVwend' of saidportion :IS-' Abeing connected with z the 'source of pressure fluid,Anot shown, and said ycircuit guard valve unit 3|).r also beingconnectedI with the'fportion |5-B of the. inlet cond-uit I5 `which leads to `andvconnectsI withthe inlet vport .i f of-the selector valve A. In `thisarrangement .5: the one circuit, guard valvev unit protects :against theloss of fluid, except for the preferably small andr substantiallypredetermined volume 'A rpreviously described and explained, in theeventof rupture at any point inthe circuit beyond the valveseat 33 of theunit 3U. It is thus unnecessary to place circuit guard valves in thecylinder conduits I5 and I1 when the arrangement of .f Fig. 5Ais'employed and said ,conduits may be directly connected to*V the fluid-motorto be acftuated; such, forl example,` as thegrnotory B of Figli.:IThis arrangementmay,therefore, bepreferred `in someinstances such,forfexample, as

` f instances in vwhich4 onlyoneselector valve. is einployed intheAcircuitor :where aplur'ality of s exa-lectorlfvalves are..` employedwith each selector if 3 "valve having aninlety conduitinwhichhthexcir'cuit guard'y valve :unitmay ,befpositionedn f nEitherxfthe `modified circuit :guardy valvey ff.: the circuitiguarda:valve: unit 30 in: the arrangef menti off Fig. 5. f .With` all of.nthesei units,` however,

i it willbe necessaryl;for the Lpilotoor" operator to w'pullfthe valvepistoxrupwardvfromfitsseatin the arrangementwof .Fig. i5"ifrupture ofthe conduit |65 occurs iwhile- .theeinlet conduit @5I ivis connected andcompletelyf'cut on "communicationfbetween duit I5 and the,conduit I 6,1the pilotk oroperator 1strokewas.1often` as desiredthereovpermitting a isubstantially; predetermined volume` -of iluid `to Vpass fromtheachambeml into.V thebore 24| I zsn, by. mst `cmmecnngy @mondain is,Awith the Y `conduit I8 ,to.,permit.the, piston 281Mo bereset unit u .5of Figi?. orzthat otfFig.elmay:beisubstituted` for f ny therewith, the.circuit vgummi .vaiv fan vworan-fclose L 1o 18 fluid motor by ,pressureduid supplied thereto through the conduitil, it would be possible andmightbe ydesirable ;to:'sti1l;.operatethewmotor in .Ethe'voppositeedirection bymeans-offpressure uid5ifadmittedxtheretowthrough the-conduit In order to effect suchIoperation of the motor, howi yever.; thea-:pilotv--or operator mustyrst-turn the valve body 24kv of.-` the 'selector valve A `toconnect therport25 ythereoffwitl'r the cylinder.v port `21V and must then pull thevalve piston out of engage- :ment with: its seat; v byvthe. meansprovided for `thispurposepaswell as `for `use in filling and bleeding;the circuit, ineach ofthe'embodimentsV .f-descrihed;v I.thereforelprefer vto use a further modied forniy of 'thepiimproved`circuit guard valve according rto'the present invention when conditions(permit itsruse and when the circuit guard valve is. disposed inn. theinlet conduit in advance ofcthe selector valve. :In this further 20-1modiiled form, means are provided by which the valve piston is moved"out ofiengagement with its l seat,y if? it should Ibe in suchengagement,each mtime A,that the connection is established between the conduit I5andvtheconduit'l orbetween y,thezoonduitf |5fandithe conduitv I1. By wayof example in Fig. 6 `I have illustrated a portion of the'modified iluidsystem together with such a 'modified form of the'circuit guard `valveunit, broadly designated bythe reference numeral 30 `33|! which willnow'be described. I f

Referring-now` tov Fig. 6, I have shown.' partly in section, a'modifiedgcircuit guard valve unit i 330`s'imilar in many respects to theunit |30 of Fig. 3` but `differing therefrom in certain particularswhich will be :pointedout presently. In the Aparticular arrangementillustrated the passage 39' of the valve unit 330 is connected with theportion `I 5-A of the inletconduit I5 which leads from' the source ofvpressure fluid, not shown, and the passage `ofsaid valve unit'330 isconnected with the portionv I5-B of said inlet conduit I5 which leadsvto and connectsfwith the inlet port 25 of` the modied selector valve AA,identical with the selector valve A of Fig. 1 except with respect' toparticulars also to be presently pointed l out. w

l Thestem |5|,v head 53, shoulder 54 and head of the modifiedvalve-piston 350 are identical with the similarly 4designated portionsof the 'valve' piston '|50 of Fig'. v 3 already Adescribed but inthisinstancefthereduced neck` portion 355 of the modied-valve-'piston350""i`ntermediate the` shoulder 54'an'dthe head-|60 doesnotcontain thepassages and {checkvalve which arepo- 55 sitioned in the 'reduced-'portion |55 floff'thel valve fwpistonfr|5|l 4of Fig( 3;" themoditledarrange- Ament of Fig/.6,y al schematically illustrated passage=3|542rv conx'ie'cts the l outer'end of the modied bore #1? i344 ofthe'modified' housing 53 I with the bore I4I 60 thereof 'andi'provided'twith aA check valve 365 Which'permits Ifluid vto passout intothe `o`ut`er end lof saidY bore-'i544butiprevents the passing of:fiuid'` infithe oppositedirection The passage 364 and the''che'ck'valvn355 `c'orres'pnondto and perform the same'functions as the passages'IBl"and I 65 f and the' clickffvalve'- `#|65 Vrespectively of Fig.'31.11-"21,Afdiag'r'ax'ninati" ll'y 'illustratedf restricted passag--3651' connects b'ore-` I4 I with the pasagees; ata inliriinnmeniatethermeck'fvaive 355fjand the"boi" A`34 Tand' thisrestrictd`v`r`passage f lfinletfconduit lisvcut off. l.Foriexample:fli'ri the v'i ,1.

the position in which it is shown in Fig. 6, as will be understood fromexplanations previously given. It will be understood, however, thatthisrestricted passage or fluid connection may, if desired, comprise aclearance between the outer diameter of the head |60 and the bore 344,as in the arrangement of Fig. 3, or any other suitable form.

A rod-like portion 359 extends downward from the head |60 in the modiedvalve piston 350 of Fig. 6 and projects through a suitable opening inthe closed end of the bore 344, suitable packing 36| being employed toprevent the outward leakage of -uid from said bore 344.

The modied selector valve AA o1' Fig. 6 is provided with a shaft 320integral with the rotatable valve body 324 thereof or suitably attachedto said valve body 324 for simultaneous rotating movement therewith anda cam member 325 positioned on the exterior of the selector valve AA ismounted on said shaft 320 and connected therewith for simultaneousrotating movement as by the key 32|. The cam member 330 is provided withfour lobes 326 separated by four portions oi reduced diameter 321, allsurfaces being preferably suitably curved to provide cam action inconjunction with the outer end of the rod portion 359 of the modifiedvalve piston 350. The arrangement is such that one of the lobes 326comes into engagement with the end of the rod portion 359 of the valvepiston 350 as the valve body 324 is turned to change connection of theinlet conduit I5 with the cylinder conduits I6 or I1, as the case maybe, if the valve piston 350 occupies a position lower than that in whichit is shown in Fig. 6, said valve piston being biased toward itsposition of Fig. 6 by spring means, not shown in Fig. 6, identical inconstruction and arrangement with the spring 13 and cooperating parts ofFig. 3. With this arrangement, whenever the rotatable valve body 324 isturned to change the connection of the conduit I5 from the conduit I6 tothe conduit Il, or vice versa, the cam 325 restores the valve piston 350to the position of Fig. 6 if it should occupy a lower position due, forexample, to rupture of the conduit with which said inlet conduit I5 hadbeen previously connected or any other cause. In all other respects themodified circuit guard valve unit 336 of Fig. 6 functions in the samemanner as` the unit |30 oiFig. 3 and the arrangement of Fig. 6 issuchthat one of the portions of reduced diameter 321 of the cam member 325is in line with the end of the rod portion 359 of the valve piston 350whenever the conduit I5 is connected with either the conduit I6 or theconduit Il in order that said valve piston may move to its extremedownward position in the event of rupture of the conduit with which itis connected, the proportions being such that the said portions 321 donot interfere with such downward movement of said valve piston 350.

While particularly suited for use in the inlet conduit in a position inadvance of the selector valve, it will be understood that the modifiedcircuit guard valve unit 330 of Fig. 6 may also be positioned at otherpoints in the circuit, such, for example, as in the conduits IB and I1.For convenience in illustration, the conduit I1 has not been shown inFig. 6 but it will be understood that said conduit I1 corresponds to andoccupies the same relative position as the conduit I1 of Fig. 1 or Fig.5.

The circuit guard valve means according to the present invention may bealso modified so that said valve will be kept openfor the substantiallyunrestricted flow of duid therethrough. in either direction of fluidflow, whenever` the requisite pressure exists in either of two iluidpressure lines, such,for example, as in either the outgoing conduit orthe return conduit. By way of example, modined circuit guard means ofthis general character are illustrated in Figs. 7 and 8 in which Fig. 7shows an enlarged view, partly in section of a modified circuit guardvalve unit 43|) and Fig. 8 shows a modified fluid system or circuitincluding modified circuit valve means or units according to Fig. 7 inthe conduits I6 and I1 respectively, together with the fluid connectionstherefor.

Referring to Fig. 7, the modified valve unit 430 is similar to the valveunit 30 of Fig. 2 from which it differs only in certain particularswhich will now be pointed out. As clearly shown in Fig. '7, a rodportion 455 extends downward from the shoulder 54 of the modiiied valvepiston 456, this valve piston 450 being identical with the valve piston50 4of Fig. 2 in all other respects. The rod portion 455 of the valvepiston 450 extends through a suitable opening in a partition 440 thatseparates the counterbore 44| from a chamber 442 formed in the modiedhousing member 43|, suitable packing 45| being used to prevent leakageof iluid around said rod portion 455 in either direction. 'I'hecounterbore 44| just mentioned corresponds with the bore 4| of Fig. 2but in this instance has been shown as of larger diameter than that ofthe throat 42 of the modified housing 43| although not necessarily so.The rod portion 455 is made of a diameter less than that of the stern 5|of the modified valve piston 450 in order that said valve piston may bemoved upward toward and into its extreme upper or fully open positionwhenever the requisite pressure exists in the chamber 38 and thecounterbore 44|, such pressure fluid acting on the lower end of theshoulder 54.

The lower end of the rod portion 455 of the valve piston 450 is arrangedto be in contact with the upper end of the dash-pot piston 60 when thevalve piston 450 and the dash-pot piston 60 occupy the positions inwhich they are shown in Fig. 7. The dash-pot piston 60 is slidable inthe bore 444 Aformed in the modiiied housing 43| and said dash-potpiston is urged toward its extreme upper position in which it is shownin Fig. 7 by a spring 63, the shoulder 443 at the inner end of the bore444 preventing further upward movement of said dash-Dot piston. Theouter end of the bore 444 is closed by a cap member 4l, shown asidentical with the similarly designated member of the embodiment of Fig.2 together with the packing 48 therefor. The dashpot piston 60 of Fig. 7is identical in construction and functioning with the similarlydesignated dash-pot piston of Fig. 2.

The chamber 442 is adapted to be connected with whichever of theconduits is the return conduit at the time that the conduit connectedwith the bosses 40 and 46 is the outgoing conduit. In the arrangement ofFig. 7 the bosses 40 and 45 are connected with the portions |6-A andIS-B respectively of the conduit I6 and hence the chamber 442 isconnected with the conduit II, as by a passage 446 in a boss 441 whichis connected with a passage 4 I 6 leading to and connecting with theconduit I1 as illustrated in Fig. 8. The point oi' connection betweenthe conduit I1 and the Jtreme upper position whenever the pressure insaid chamber equals or exceeds the value necessary yfor thispurpose.

Thevalvepiston 450 of the valve unit 430 may thus 4be moved toor held inits extreme upper, position by action of pressure fluid in either theconduit I6 or |1. This is also true `with respect to the circuit guardvalve unit 430' of` Fig. 8, here presumed to be identical with the unit430, which is shown as positioned in the conduit |1 and having its boss441 connected with the conduit I6 as by the passage 4|1. The arrangementmay thus be made such that`both of these valve units will be kept openwhenever there is flow of fluid through the conduits I6 and |1, and thismay frequently be desirable. For example, the arrangement may be madesuch that back pressure inthe conduit I1 caused by exhaust of iiuid fromthe motor B through the conduit |1 would keep the valve unit 430 openeven during overrun ofthe piston I of the motor B, notwithstanding thatthe pressure in the conduit I6 might drop to a low value during suchoverrun. Also,

pressure in the conduit I6 would keep the valve unit 430 open duringexhaust of fluid through the conduit |1, thus assuring minimumresistance to flow through said unit 430' in this direction of iluidiiow. y

In all other respects the circuit guard valve unit 430 of Fig. 'Ifunctions in substantially the same manner as the valve unit ,30 of Fig.2 as already explained and will close to limit the loss of fluid fromthe system in the event of a rupture therein.

With the arrangement made such as described in Ithe preceding paragraph,if the rupture occurs v in the outgoing conduit, that is to say, theconduit conveying pressure uid to the motor B, during overrun of thepiston `Ill of the motor B, the amount of fluid escaping will equal thevolume passing through the outgoing conduit while the correspondingcircuit guard valve 430 or 430' therein is held open by back pressure inthe other of said conduits, that is to say, by back pressure in thereturn conduit, caused by exhaust of` fluid from the motor during suchoverrun, plus the volume permitted to pass through the circuit guardvalve unit in the outgoing conduit during the retarded downward movementof the valve piston 450 until its fully closed position is reached.

The circuit guard valve means according to the present invention may befurther modified to provide such means capable of safeguarding againstexcessive loss of fluid due to rupture in any one of a plurality ofconduits. By way of example, a modified arrangement of .this generalcharacter is illustrated in Fig. 9 in which the circuit guard valvemeans is shown as arranged to f valve means 30 of Fig. 2 and accordinglyhave safeguard against excessive loss of fluid from the system in theevent of rupture of either of two uid conduits.

Referring to Fig.`9 the modiiled circuit guard valve means broadlydesignated by the numeral 530 has been shown as connected with theportions IS-A and IG-B respectively of the conduit I6 and with theportions |1-A and |1-B of the conduit |1 which may be similar to thecorrespondingly designated conduits of Figs. 1 and 8,

been designated by the samereference numerals.

The valve means 530 of Fig. 9 is contained within a two-part housinghere shown as comprising a housing member 3| identical with thesimilarly designated housing of Fig. 2 and also a housing member 53|.The housing member 3| is provided with a dash-pot piston 60 slidablewithin the bore 44 of said housing member 3| and identical inconstruction with the dash-pot piston 60 of Fig. 2, and `likewisefunctioning in the same manner. A spring 63 urges the dash-pot piston 60of Fig. 9 into its extreme inward position in which it is shown, in thesame manner as explained in connection with Fig. 2. The outer end of thebore 44 is closed by a cap member 41 together with packing 48 which arealso identical with the similarly designated members of the embodimentof Fig. 2.

In the modied housing 53| the bore 54|, which corresponds to the bore 4Iof the housing 3|, terminates in a partition 540 which separates saidbore 54| from a central opening 542 in the modied end portion 544extending into and closing the bore 32 of said housing 3| of Fig. 9substantially as illustrated, the two housing members being heldtogether by threaded engagement with one another as shown. The portionsof the housing member 53| just mentioned take the place of the bore 44of the housing'member 3|, as clearly shown in Fig. 9 but in all otherrespects the housing member 53| is identical with said housing member3|. Suitable packing 543 is provided to prevent leakage around the outercircumference of the housing members and portion 544.

The circuit guard valve means of Fig. 9 includes valve piston means hereshown as a twopart piston structure comprising a valve piston member`broadly designated by the numeral 555 and a valve piston member broadlydesignated by the numeral 580. The valve piston member 550 includes ahead 53, a shoulder 54 and a reduced end portion 55 identical with thesimilarly designated portions of the valve piston 50 of Fig. 2 and,similarly, the arrangement is such that the tip of said reduced endportion 55 is in contact with the adjacent end of the dash-pot piston 60when the parts occupy their positions of Fig. 9. The valve piston member550 is slidably supported by its stem 55| which extends from the head 53and enters the central opening 542 in the end portion 544 of the housingmember 53|, suitable packing 532 being employed to prevent leakagearound said stem 55|. The end of the stem 55| terminates in a reducedportion 556 having a diameter less than that of the stem 55| andextending through a suitable opening in the partition 540 into the bore54| of the housing member 53|, suitable packing 543 being employed toprevent leakage around said reduced portion 556. The end of the stem 55|is adapted to be exposed to atmospheric pressure and the space in thecentral opening 542 intermediate the end of said stem 54| and thepartition 540 is accordingly connected with the atmosphere as by apassage 541. e e

The valve piston member 580 includes a stem 58| having a diametergreater than the diameter of the reduced portion 555 of the valve pistonmemberc550 but less than the diameter of the shoulder 884, and as hereshown the diameter of the stem 58| is the same as the diameter oi thestem 55|. but not necessarily so. The valve piston 58u also includes ahead 883 and the shoulder 584 above mentioned which correspond with andare here shown as substantially identical with the head 53 and shoulder54 respectively of the valve piston member 558. The valve piston member580 is slidably supported by its stem 58| in the central opening of agland 34. identical with the gland 34 of the embodiment of Fig. 2, saidgland 34 of Fig. 9 being held against inward displacement by a shoulder35 and also being -held against outward displacement by a hollow capmember 510 in threaded' engagement with the outer end of the bore of themodiiied housing member 53|. Suitable packing is provided to preventleakage around the gland 34 and stem 55|, here illustrated by thepacking 38 and 52 respectively.

The valve piston members 550 and 588 are arranged to be connected forsimultaneous axial movement. cordingly also includes a rod portion 551of smaller diameter than and extending from the reduced portion 558 ofsaid valve piston member 558, said rod portion extending entirelythrough the valve piston member 580 which is provided with a suitablecentral opening for this purpose, packing 558 being employed to preventleakage around said rod portion 551. Similarly, the end of the valvepiston member 580 adjacent the shoulder 584 thereof terminates in apreferably tapered portion 585 adapted to be in contact with a Washer558 which in turn bears against the preferably spherical surface 555formed on the end of the reduced portion 558 of the valve piston member550. The two valve piston members are held together for simultaneousaxial movement by means of a. nut 588 and a jam or lock nut 581 on thethreaded end of the rod portion 551 of the valve piston 558, the nut 588bearing against a washer 588, which in turn bears against the preferablyspherically shaped end of the valve stem 58|, the arrangement thus beingsuch as to permit limited universal and radial adjusting movement of thevalve piston member 589 relative to the valve piston member 550 so as toprevent binding of the parts and permit both of the heads 53 and 583 toengage their respective valve seats 33 in fluid tight engagement whenthe valve piston means occupies its fully closed position. It is for thesame reason that the above described washer and spherical surfacearrangement is preferably provided at the end of the reduced portion 558of the valve piston'member 550. With this arrangement the two valvepiston members 550 and 580 will move axially in unison with one anotherand the arrangement is further made such that the heads 53 and 583 ofthese valve piston members come into fluid tight engagement with theirrespective valve seats 33 simultaneously and also such that theshoulders 54 and 584 occupy the same relative positions with respect tothe respective throats 42 of the valve means.

The valve piston means of Fig. 9 is biased toward the position in whichit is shown by the springs 83 and 13 in substantially the same manner asexplained in connection with the valve piston 50 of Fig. 2. The spring83, acting through the dash-pot piston 60 of Fig. 9, serves to urge thevalve piston means toward its position of Fig. 9 ii displaced therefromin a direction toe, ward movement The valve piston member 550 acward thecap member 41. Similarly, the spring 13 disposed/in the interior of thecap member 510 urges the valve piston means toward its position of Fig.9 if displaced therefrom in a direction away from the cap member 41; forthis purpose, the outer end of the cap member 810 is provided with aninternal ilange 81| against which the outer end of said spring 13 bears.The inner end of the spring 13 bears against a modified abutment pieceor spring retaining cup 514 having an internal Yflange 515 arranged toengage the jam nut 581`when the valve piston means of Fig. 9 isdisplaced from its position thereof in a direction away from the capmember 41: the gland 34 acts as a stop preventing further inof theretaining cup member 514 and hence limits the extent to which saidspring 13 can urge or move the valve piston :n'eans in a directiontoward the cap member With this modiiied arrangement as shown in Fig. 9and with the parts in the positions shown therein, the valve pistonmeans will be moved away from the cap 41 and toward its fully openposition by the requisite pressure in either the bore 4| or the bore 54|and will be held in its fully open position whenever the requisitepressure exists in either the conduit I8 or the conduit I1; in thisrespect the arrangement of Fig. 9 functions in a manner generallysimilar to that of Fig. 7..

The valve piston means will be moved to bring its heads 53 and 583 intoengagement with their respective seats 33 upon rupture of whichever ofthe conduits is the outgoing conduit and upon the drop in the pressuresin both conduits below the pressure required to hold said valve pistonmeans toward its fully open position and away from the position in whichit is shown in Fig. 9. Upon such rupture and pressure drop, the pistonvalve means will move from its position of Fig. 9 to its fully closedposition at a relatively retarded rate of movement determined bydash-pot action of the dash-pot piston in the same general manner asexplained in connection with the embodiment of Fig. 2 so that under mostconditions of operation the volume of iiuid permitted to escape from theoutgoing line is thus limited to the substantially predetermined volumepermitted to pass through said line and the circuit guard valve meansduring this interval. As in the embodiment of Fig. 'l however, in caseof overrun of the piston I0 of the motor B, the uid exhausted by saidmotor during such overrun may hold the heads 53 and 583 valve pistonmeans out of engagement with their respective valve seats 33 if thereturn conduit is not ruptured; in the event oi' rupture of the outgoingconduit during or prior to such overrun of the motor B, 'the maximumiiuid loss from the outgoing conduit would then comprise the volume ofoutgoing iiuid permitted to pms through the circuit guard valvefmeans530 during overrun and the volume thereof permitted to pass through saidcircuit guard means 538 during the interval of relatively retardedmovement of the valve piston means from its position of Fig. 9 to itsfully closed position.

To facilitate filling and bleeding of the circuit or the like, themechanic may hold the valve piston means of Fig. 9 in its fully openposition by grasping with pliers or the like the reduced end portion 558of the rod portion 551 of the valve piston member 550, the pliers orother tool being inserted through the hole 512 in the cap member i"dite! removing the cover l1! ju"st mentioned may tend t vprogre'ssii/elyincrease shownffforfp with a modied form of the circuit guard valve A gping. ,.:zladukewiseft offili'ustraton in"connectionVVA 75 of Figs. 2and 3, suitable packing being used to valvepiston head Serves shbulder 4ena o the mations-offici Offb meansfjoi s In :this: the mod-med 5011sprovidedffwith a relatively' .01'11"4 narrQWs; heed-15.4 `hef/vinse!!diameter thantthatpithe stemaileand.lessthan that 0MM 5 modiedithrcatijllzj therelativediametersxctsaida and ,saidfthroat-qm;frbeingffsuch ias `tu 5: provid y hel desired restarleted;`connectionlbetween f J :the chamber 3,8 .jandzthek chamber arbore'lili-ac said -fvalye -`piston 5|L m0vesf,downward`V from its l 0position .ci'f'Figz 11 Theghead J54--of:Iig.:11-fthusjubstantially thesamernpurpose im thel j n, n l y1reduced.,portion 152 sep-e 'fffaratesfv-thefheadl 5,4 fromthehe'ad lzfe'thefmodtv ined valvefpistcnl150. 'and fsimilarlyxan end pore 5 ticn 'l5` vfeprjectsydownward:from-fthe head1: 15|

and .thearrangement isfsuchithat the-ztip of lsaid f portion .1155115 in'gcontact withthezvupper end. c;Ldvashpot` piston 60;:.whenvthemat`s:are ini: l, i or ilwerpositiosd 20 throetgjlglgisheregshownasicf:substantially uni-w `L- forni qiameter;falthcughsrnotnecessarily- `so, oftsuchflength'- theft -the`f:headf1154remains inl saidy ihr t pltthroughqlltffthe, downwardacmovement nvelyepiston .150;fr0m tsfpositinffP18911?? toyitsf fullyclosedlvppsitionf.' -*With .ithisfiniodied armngemenwthe resistance to:the `frias'sinfr44 cf -l fluidk gthrcugh,-.gtherestrictedconnectimprovided i :,by. thecleara'nce space;betweethez'hadBland the; :throat :fMZ; "remains :asubstantilly c'stant throughout-thedownward."movement'offthe valve pistoni '.150 from' its lpositionfIoflI-Fig '-1'1.1In""Son`1`e instances:thiss:constructionnajglsoiesult'"a .izfsmeunreduction fin thewightffof-fth As samidiameter/bt this isnotrneices'sarily 'the cs'f as will be understood from previousexplangtions'.

27 prevent leakage past said gland and pt said stem as indicated at 38and 62.

The gland 34 of Fig. 12 is held against outward displacement by a capmember identical with the cap member |18 of Fig. 3, within which are aspring 13, retaining cup member |14. abutment piece |12, rod` |80 andassociated parts. all identical with the similarly designated members ofthe embodiment of Fig. 3 and functioning in the same manner. Thearrangement of Fig. 12 is thus such that the valve piston 858 is biasedinto the position in which it is shown in this ligure whenever thepressures in the chamber 838 and the bore 84| are substantiallyequalized and are below a predetermined value. as will be understoodfrom explanations previously given.

Downward movement of the valve piston 850 from its position oi Fig. 12is controlled by regulation or control of admission of fluid to thechamber 839 situated intermediate the upper end of the body portion 852and the gland 34. In the particular embodiment illustrated in Fig. 12the arrangement is such that the valve piston 85|! ,remainssubstantially stationary during a substantially predetermined intervalbefore commencing its downward movement fromits position of Fig. 12toward the seat 833 and then moves quickly to its fully closed position,this being accomplished by control of admission oi fluid to the chamber839 by means oi valve mechanism which will be understood from anexplanation of the manner in which it functions. For purposes of thisexplanation it' will be assumed that the valve piston 850 occupies itsposition of Fig. 12 and that the portion |8-A oi the conduit |8'has justbeen connected with the source of pressure fluid, as by connection withthe conduit I5 of Fig. 1.

Under the conditions just mentioned, iluid will pass into the chamber838 and thence, through the restricted connection provided by theclearance space between the shoulder 854 and the throat 842, into v'thechamber or bore 84|. If the portion of the circuit or system directlyconnected with the bore 84| is intact (i. e. free from rupture, etc.)and illled with fluid, pressure will be built up in the chamber 84|almost instantly and this pressure, acting on the lower end of the valvepiston 858, will almost instantly move said valve piston 850 upwardtoward its fully open position to permit the substantially unrestrictedpassing of fluid through the circuit guard valve means or unit 838. Uponsuch upward movement of the valve piston 858 iluid passes out of thechamber 833 into the chamber 838, the path of iiow including a portionof the passage 818, the passage 81| and the passage 812. the check valve813 in said passage 81| opening to permit the ow of iluid in thisdirection but preventing the passing of uid therethrough in the oppositedirection. It will be understood that upward movement of the valvepiston 850 will take place whenever the pressure in the chamber 84|reaches the required value.

Under the conditions assumed -for purposes of explanation, uidwill alsopass from the chamber 838 into the adjacent end of the bore 88| of thecylinder member 868, this path oi' now including the passage 812, aportion of the passage 81|, portions of the passage 815, the passage 811and a suitable opening in the end cover 882 which closes this end of theIbore 88| In this direction of flow. the check valve 816 in the passage815 prevents the passing of iluid therethrough so that the iluidentering the end of the 28 bore 88| adjacent the cover member 882 ishunted to the volume which may pass through the restricted connection orpassage in the passage 811, this restricted connection being hereschematically illustrated as a variable orice 818 which may be varied toprovide any desired extent of opening, as by the schematicallyillustrated varying means 819. Pressure fluid entering the bore 88|through the path of ow just described acts upon the adjacent end of avalve piston or plunger 888 which is slidably tted within the bore 882and is here shown as hollow to receive one end of a spring 881 whoseother end is received in asuitable reduced bore 884 of the cylindermember 888. 'I'he spring 861 is preferably light but of suicientstrength to quickly return the plunger 888 to its position of Fig. 12when the pressures on the opposite ends of said plunger aresubstantially equalized. The plunger 888 will be moved toward the rightas viewed in Fig. 12 by pressure iluid thus admitted to the bore 88| andits rate of movement will depend upon the rapidity with which pressureiluid may pass through the orifice 818 which (in applications of thegeneral character previously mentioned) is preferably made such or soadjusted that the iluid passing therethrough produces relatively slowmovement of the plunger 888 toward the right. Fluid in advance of theplunger 888 as it moves toward the right is exhausted through a suitableopening in the end cover 863 which is appropriately connected with apassage 880 leading to and connecting with a passage 88|, one end ofsaid passage 88| connecting with the passage 810 and the other endthereof connecting with the passage 882 which in turn connects with thepassage in the modied housing 83|. Fluid exhausted in advance of theplunger 868 will thus pass into the passage 45 as its pressure will berelatively low and insufllcient to open the check valve 885 in thepassage 818, said check valve being held closed by pressure on the sidethereof directly connected with the chamber 833. It may here be notedthat some pressure will exist in the chamber 833 under the conditionsnow being considered, this pressure being caused by action of thepressure iluid upon the beveled face 853 of the valve piston 850, butsuch pressure in said chamber 839 will be lower per square inch thanthat in said chamber 838 due to the fact that the net eilective area ofthe beveled face 853 is less than the nt effective area oi' the upperend of the body portion 852 in said chamber 839.

'I'he bore 88| of the cylinder member 880 is provided with an annularcounterbore or port 865 which is connected with the passage 81| by apassage 883 leading to and connecting with the passage 81| and said boreis also provided with an annular counterbore or port 888 which isconnected with the passage 810 by the passage 884. It will be observedthat the plunger 888 covers both oi the ports 885 and 888 when saidplunger is in its position of Fig. l2 and will continue to cover themuntil said plunger has been moved therefrom a considerable distancetoward the right, the arrangement being such that no iluid may passthrough said ports as long as they are covered by said plunger.

The plunger 888 will continue its relatively slow movement toward theright, at a rate determined by the rapidity with which iluid is admittedto the bore 88| through the orifice 818. during an interval until theleft end of said plunger 868 uncovers the port 888. Immediately uponthis un covering oi' the port 865 pressure fluid `vill be admittedtherethrough relatively rapidly into the bore 88|, whereby the plunger888 will be moved relatively rapidly through the remainder of its pathof movement toward the right and into its extreme position at the right,in which position the left end of said plunger 888 is disposed to theright of the port 888. so that said port 868 is fully uncovered and isconnected with the port 888. Fluid connection is thus establishedbetween the chamber 838' and the chamber 839.

During'the interval of movement of the plunger 888 from its position ofFig. 12.unti1 it uncovers the port 888. uid will have continued to passfrom the chamber 838 into the bore 84| through the restricted connectiontherebetween and will build up in said chamber 84| pressure sufllcientto move the valve piston 858 upward from its position of Fig. 12 if theportion of the circuit directly connected withl said chamber 84|isintact, normal leakage from this portion of the circuit beingreplenished during this interval. If, however. the fluid passing intothe bore 84| during this interval does not build up therein the pressurerequired to move the valve piston 888 upward from its position of Fig.12, as due, for example, to rupture of the portion I8-B of the conduitI8, the valve piston 858 will remain substantially stationary in itsposition of Fig. 12 during said interval. Under the condition justmentioned, the valve piston 858 will be moved downward to its fullyclosed position substantially instantly after the plunger 868 uncoversthe port 868 and thereby establishes fluid connection between thechambers 838 and 839; the force then acting to move said valve piston858 downward is equal in amount to that produced by the force exerted bythe pressure fluid upon an area equal to the difference between thecross-sectional areas of the shoulder 854 and the stem 85| of said valvepiston 858. The maximum volume of fluid thus permitted to pass throughthe restricted connection between the chamber 838 vand the |bore 84|,unless the pressure required to move the valve piston 858 upward fromits position of Fig. 12 is built up in the bore 84|, is thus determinedby the volume that may pass through said restricted connection duringtheinterval of movement of the plunger 888 from its position of Fig. 12until it uncovers the port 888 and hence said volume may be limited to asubstantially predetermined and controlled amount by' means of theorifice 818,

which in the 4particular arrangement illustrated may be adjusted to anydesired extent.

As in the embodiments previously described, this maximum volume will beheld closely approximately, if not exactly, to the predetermined amounteven though the viscosity of the circulated fluid may change and eventhough there may be a change in the pressure of the fluid in the chamber838 during the interval above mentioned. In this instance, change inviscosity will correspondingly (although not necessarily exactly) changethe relative resistance to flow through the restricted connection|between the chamber 888 and the bore 84| and through the orifice 818and, similarly, change in pressure of the fluid in the chamber 838 willcorrespondingly (although not necessarily exactly) change the relativerapidity with which fluid will pass through said restricted connectionand said orifice. The duration oi' the interval in which the restrictedconnection is maintained between the chamber 838 and the bore 44| isthus modified conformably with the rapidity with which uid -of movementof the plunger 888 from its position of Fig. 12 until it uncovers theport 868 which. in turn, is modified by modification of the rapiditywith which fluid passes through the oriilce 818.

The valve piston 858 will be substantially instantly reset to itsposition of Fig. 12, irrespective of whether it occupies a higher or alower position, when the pressures in the chamber 888 and in the bore84| drop below a value determined by the spring 'I3 as, for example,when the conduit I8 ls connected with the exhaust conduit I8 of Fig. 1,as will be understood from explanation previously given. If the valvepiston 858 is below its position of Fig. 12 at the time of suchresetting, the consequent upward movement thereof will cause fluid to beexhausted from the chamber 839 into the chamber 838, said fluid passingthrough the passages 818, 81| and 812 and through the check valve 813which permits the flow of fluid therethrough in this direction asalready mentioned. If, however, at the time of resetting, the valvepiston 858 occupies a position above that in which itis shown in Fig.12, the consequent downward movement thereof will tend to create avacuum in the chamber 839, under the influence of which fluid will passfrom the passage 45 into the chamber 839, said fluid passing through thepassages 882, 88| and 818 and through the check valve 885 which isarranged to readily open to permit the flow of fluid in this direction.y

The plunger 888 will also be reset to its position 'of Fig. 12substantially instantly upon substantial equalization of pressures inthe opposite ends of the bore 88|. The fluid in advance of the plunger888 as it is thus moved toward the left during such resetting passes outquickly and against substantially little resistance into the chamber838, said fluid passing through the passages 815, 81| and 812 andthrough the check valve 818 which is arranged to open to permit thepassing of fluid therethrough in this direction.

It will be understood that the pilot or operator may reset the valvepiston 858 and the plunger 888 to their positions of Fig. 12 as often asdesired by, for example, connecting the conduit I8 with the exhaustconduit I8. For each such resetting the circuit guard valve means 838 ofFig. 12 will permit a controlled and limited or substantiallypredetermined volume of fluid to pass from the chamber 838 into the bore84| unless the pressure in said bore 84| is built up to the valuerequired to move the valve piston 858 upward from its position of Fig.12, to thereby provide substantially unrestricted flow of fluidtherethrough with little or substantially no resistance to ow.

In the direction of fluid flow opposite to that just considered, that isto say, when fluid passes from the bore 84| into the chamber 838, as,for example, when fluid is being exhausted through the conduit I6 by themotor B of Fig. 1, the fluid in the bore 84| acts upon the lower end ofthe valve piston 858 and moves said valve piston 858 upward from itsposition of Fig. 12. With the conduit I8 connected with the exhaustconduit I8 of Fig. l, substantially no pressure exists in the chamber838 and the principal resistance to upward movement of the valve pisthevalve piston 858 from the position in which it is shown to its extremedownward or fully closed position and thus provide the desired intervalof restricted iiuid connection between the chamber 838 and the bore 84|before said valve piston cuts off communication therebetween. With themodified means illustrated in Fig. 13 the above mentioned interval isprovided by causing the valve piston to be moved downward at acontrolled and usually relatively slow rate oi movement as said valvepiston moves from the position in which it is shown to its fully closedposition.

As in the embodiment of Fig. 12, however, the arrangement of Fig. 13 issuch that the valve piston 858 will be moved quickly upward from thepositon in'w'hich 'it is shown and toward its fully open positionwhenever the required pressure exists in YVthe bore 84|. It will beunderstood that the pressure just mentioned may be built up in thechamber or bore 84| by fluid passing into said bore from the chamber 838through the restricted connection therebetween provided by the clearancespace intermediate the shoulder 854 and the throat 842', as in thearrangement of Fig. 12. Upon upward movement of the valve piston 858fluid passes out of the chamber 839 into the chamber 838 through thepassages 898, 89| and 892 and through the check valve 893 in the passage89| which permits the ow of fluid therethrough in this direction only.

For purposes of iurther` explanation it will be assumed that the valvepiston 858 occupies the position in which it is shown and that the sameconditions exist as were assumed for purposes of explanation inconnection with the arrangement of Fig. 12. Under these conditionspressure uid from the chamber 838 passes into the chamber 839, the path.of ow including the passages 892, 894 and 898. The passage 894 isprovided with a restriction which is here schematically shown as avariable orice 895 which may be adjusted or opened to any desired extentas by the schematically illustrated means 898. Fluid is prevented frompassing from the passage 898 into the passage 888 by the check valve 891which permits iluid to pass therethrough only in the opposite direction.The iluid thus entering the chamber 839 will cause the valve piston 858to move downward and the rate of this downward movement of the valvepiston 858 is determined by the rapidity with which fluid is admitted tosaid chamber 889 which in turn is determined and controlled by therestriction or oriiice 89S, the latter being capable of adjustment toany desired extent in ,the particular embodiment as above stated. Thearrangement is such that the rate at which the riice 895 permits iiuidto enter the chamber 839 causes downward movement of the valve piston858 at a rate providing the desired interval of restricted uidconnection between the chamber 838 and the bore 84| between the timethat said valve piston commences its downward movement from the positionin which it is shown until it reaches its fully closed position. Asexplained in connection with the embodiment of Fig. l2, however, thisinterval is modified conformably with change in the rapidity with whichfluid passes through the restricted connection between the chamber 888and the bore 84| and this is the case regardless of whether the changein the rate of ow through this restricted connection is caused by changein viscosity of the circulated iiuid or by change in the pressureexisting in the chamber 838. The arrangement of Fig. 13 thus controlsand limits to a substantially predetermined volume the maximum volume ofuid Y that may pass from the chamber 838 into the bore 84| for eachresetting of the valve piston 858 unless, ofrrcourse, said valve pistonis moved upward by pressure built up in the bore 84| as will be fullyunderstood from previous explanations. It will also be understood thatthe valve piston 858 will be reset to the position in which it is shownwhenever the pressures in the chamber 838 and the bore 84| aresubstantially equalized at a pressure below a predetermined value andthat said valve piston may be reset by the pilot or operator as often asdesired.

Upon downward movement of the valve piston 858 from a position abovethat in which it is shown, iiuid may pass into the chamber 839 from thepassage 45, such uid passing through the isigsages 898 and 898 andthrough the check valve The modied means of Fig. 13 thus functions insubstantially the same manner as the means of Fig. 12 except, of course,that with the arrangement of Fig. 13 the valve piston 858 moves down- Y'ward at a controlled and usually relatively slow rate of movement as itmoves from the position in which it is shown to its fully closedposition to thereby provide the desired interval of restricted fluidconnection between the chamber- 838 and the bore 84| as above explained.

or biased to the position in which it is shown upon rupture of theportion of the circuit Aor system directly connected with the bore orchamber 84| and consequent drop on the pressure in the conduit I6 belowthe value determined by the spring 13. If the portion IG-A of theconduit I8 is connected with the supply conduit I5 at the time of suchrupture, the circuit guard valve means 838 will function in the samemanner as explained in the foregoing explanations in which it wasassumed that connection had just been established between the supplyconduit |5 and the portion |6-A of the conduit I8, the circuit guardvalve means 838 limiting the volume of fluid that may unintentionallyescape from the outgoing conduit in the event of such rupture as will beunderstood from previous explanations.

Each of the embodiments illustrated has its particular advantage. someof which have been pointed out. In all embodiments, however, loss o1iluid from the outgoing conduit is limited in the event of rupturethereof and the volume permitted to escape in such event is controlled,assuring that the available supply of iluid in the system or circuitwill not be seriously depleted. Also in all embodments the valve pistonmeans moves to its fully open position where it presents little or noresistance to ow whenever the requisite pressure exists in the conduitwith which it is connected. f

While the present invention has been described and is particularly wellsuited for use in connection with a system employing a liquid, such, forexample, as oil, as the circulated uid, it is understood that certainfeatures thereof may also be employed in connection with systems inwhich the circulated iluid is a compressible uid such,

